[PATCH v10 0/9] Hyper-V: paravirtualized remote TLB flushing and hypercall improvements

Vitaly Kuznetsov vkuznets at redhat.com
Mon Nov 6 10:10:00 UTC 2017

Wanpeng Li <kernellwp at gmail.com> writes:

> 2017-11-06 17:14 GMT+08:00 Vitaly Kuznetsov <vkuznets at redhat.com>:
>> Wanpeng Li <kernellwp at gmail.com> writes:
>>> 2017-08-03 0:09 GMT+08:00 Vitaly Kuznetsov <vkuznets at redhat.com>:
>>>> Changes since v9:
>>>> - Rebase to 4.13-rc3.
>>>> - Drop PATCH1 as it was already taken by Greg to char-misc tree. There're no
>>>>   functional dependencies on this patch so the series can go through a different tree
>>>>   (and it actually belongs to x86 if I got Ingo's comment right).
>>>> - Add in missing void return type in PATCH1 [Colin King, Ingo Molnar, Greg KH]
>>>> - A few minor fixes in what is now PATCH7: add pr_fmt, tiny style fix in
>>>>   hyperv_flush_tlb_others() [Andy Shevchenko]
>>>> - Fix "error: implicit declaration of function 'virt_to_phys'" in PATCH2
>>>>   reported by kbuild test robot (#include <asm/io.h>)
>>>> - Add Steven's 'Reviewed-by:' to PATCH9.
>>>> Original description:
>>>> Hyper-V supports hypercalls for doing local and remote TLB flushing and
>>>> gives its guests hints when using hypercall is preferred. While doing
>>>> hypercalls for local TLB flushes is probably not practical (and is not
>>>> being suggested by modern Hyper-V versions) remote TLB flush with a
>>>> hypercall brings significant improvement.
>>>> To test the series I wrote a special 'TLB trasher': on a 16 vCPU guest I
>>>> was creating 32 threads which were doing 100000 mmap/munmaps each on some
>>>> big file. Here are the results:
>>>> Before:
>>>> # time ./pthread_mmap ./randfile
>>>> real    3m33.118s
>>>> user    0m3.698s
>>>> sys     3m16.624s
>>>> After:
>>>> # time ./pthread_mmap ./randfile
>>>> real    2m19.920s
>>>> user    0m2.662s
>>>> sys     2m9.948s
>>>> This series brings a number of small improvements along the way: fast
>>>> hypercall implementation and using it for event signaling, rep hypercalls
>>>> implementation, hyperv tracing subsystem (which only traces the newly added
>>>> remote TLB flush for now).
>>> Hi Vitaly,
>>> Could you attach your benchmark? I'm interested in to try the
>>> implementation in paravirt kvm.
>> Oh, this would be cool) I briefly discussed the idea with Radim (one of
>> KVM maintainers) during the last KVM Forum and he wasn't opposed to the
>> idea. Need to talk to Paolo too. Good thing is that we have everything
> I talk with Paolo today and he points this feature to me, so I believe
> he likes it. :) In addition,
> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
> I search Hypervisor Top Level Functional Specification v5.0b.pdf
> document but didn't find a section introduce the Hyper-V:
> paravirtualized remote TLB flushing and hypercall stuff, could you
> point out?

It's there, search for
HvFlushVirtualAddressSpace/HvFlushVirtualAddressSpaceEx and


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